OCB is a friendly fork of Odoo 8 and is not merged back into the main branch.

It contains the standard version of Odoo + unmerged bugfixing that are not yet accepted/treated in standard Odoo.

It is been tested through OCA Continuous Integration server so it is reliable and fully usable in production environment. Besides per se, it contains more bug fixing than the standard branch.

You should be able to use a standard DB from Odoo 8 into OCB (and vice-versa). Normally bug fixing should not impact the data model but slight difference might appear. Nevertheless, you should test it thoroughly before proceeding in production environment.